An optical recording medium employing laser makes storage and reproduction of high density information records possible, and its development have been remarkable recent years.
As an example of the optical recording medium, an optical disc may be mentioned. In general, an optical disc is usually designed to irradiate a focused laser beam of about 1 .mu.m, to a thin recording layer formed on a substrate of disc shape to conduct high density information recording. The recording is carried out in such a manner that upon absorption of the layer beam energy, the irradiated portion of the recording layer will undergo a thermal deformation such as decomposition, evaporation or melting. Reproduction of the recorded information is carried out by reading the difference in the reflectance between the portion having a deformation formed by the laser beam and the portion having no such deformation.
Accordingly, an optical recording medium is required to efficiently absorb the energy of the laser beam, and also required to have a predetermined amount of absorbed light to a laser beam having a specific wavelength employed for recording and to be high in the reflectance to a laser beam having a specific wavelength employed for reproduction for accurately conducting the reproduction of information.
As the optical recording medium of this kind, there have been proposed ones comprising an organic dye thin film formed on a substrate. Since it is possible to form the organic dye thin film by coating, its mass productivity is high and the cost is expected to be low.
It has been known that a thin film containing the cyanine type dye is employed as the organic dye thin film (reference can be made with Japanese Unexamined Patent Publications No. 112790/1983, No. 114989/1983, No. 85791/1984 and No. 83236/1985). However, the optical recording medium comprising such a cyanine type dye is poor in the light stability, and has a problem in the storage stability and a drawback such that it is prone to light deteriorating upon reproduction. Thus, Japanese Unexamined Patent Publications No. 55795/1984, NO. 40389/1989, No. 55189/1990, No. 68742/1990, etc. propose to add various metal chelate compounds represented by the following structural formula (1), (2), (3) or (4), to the cyanine type dye to improve the light stability. However, the improvement is still on an insufficient level. ##STR2##